code: def test_init_with_extra_headers(argilla_user: User):
      expected_headers = {
          "X-Custom-Header": "Mocking rules!",
          "Other-header": "Header value",
      }
      argilla.client.singleton.init(
          api_key=argilla_user.api_key, extra_headers=expected_headers
      )
      client = active_client()
  
      for key, value in expected_headers.items():
          assert (
              client.http_client.headers[key] == value
          ), f"{key}:{value} not in client headers"
  
file_path: argilla/tests/integration/client/test_init.py
imports: import argilla.client.singleton
  import pytest
  from argilla.client import api
  from argilla.client.models import TextClassificationRecord
  from argilla.client.singleton import active_api, active_client
  from argilla.server.models import User
  from tests.factories import UserFactory, WorkspaceFactory
  from tests.integration.utils import delete_ignoring_errors
label_desc: Use image node_id 2 for calling a global function with example usage: test_init_with_extra_headers(argilla_user) without return types